virtiofsd: Call qemu_init_exec_dir

Since fcb4f59c87 qemu_get_local_state_pathname relies on the
init_exec_dir, and virtiofsd asserts because we never set it.
Set it.

Reported-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20201002124015.44820-1-dgilbert@redhat.com>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/passthrough_ll.c

@@ -2839,6 +2839,8 @@ int main(int argc, char *argv[])
     /* Don't mask creation mode, kernel already did that */
     umask(0);
 
+    qemu_init_exec_dir(argv[0]);
+
     pthread_mutex_init(&lo.mutex, NULL);
     lo.inodes = g_hash_table_new(lo_key_hash, lo_key_equal);
     lo.root.fd = -1;